This invention relates to rapid texture prototyping, i.e., to the production of textured prototype which can simulate the appearance and feel of an article. The invention also embraces the production of copies of the textured prototype.
Many moulded articles are made with a textured surface finish. Examples include interior trim parts for automobiles, knobs and handles for cooking utensils, garden furniture, casings for audio and video equipment, computers and calculators, and so on. Many of these items are made from large, expensive moulds. The moulds are first made with a smooth moulding cavity which must then be etched to produce the texture. Etching is done by applying a resist and immersing the mould in acid etchant.
Once etched, it will usually be impossible, or at best highly impracticable, to expunge the texture and apply a different texture. It is vital, therefore, for a designer to have some idea of how the product will look, textured. To this end, computer simulations are proposed in which the item can be imaged to a screen using CAD techniques and a texture superimposed. No matter to what state of excellence this type of simulation can be raised, however, it still cannot give the designer a textured, truly three dimensional component to build into a prototype assembly of, say, an automobile.
Furthermore, it is desirable that a number of copies of a prototype can be made, using the original rapid prototype as a formative model.
Various methods are known by which rapid prototypes can be produced using computer aided design (CAD) software to generate three dimensional (3D) prototype designs. In stereolithography, a tank containing a resinous, UV sensitive polymer is selectively cured by UV radiation from, for example, a laser. The laser follows the CAD data profile to selectively cure the resin, building up layers of solid substrate. This procedure is accomplished by cross sectional xe2x80x9cslicingxe2x80x9d of the 3D CAD data to produce laminae of, for example, 0.1 mm thickness. The resin containing tank has a table positionable below the surface of the resin by an amount equal to the thickness of the lamina. The laser beam is tracked across this layer of resin to produce a thin layer of cured resin which is equivalent to the cross sectional CAD lamina. The table is then covered by an amount equal to the thickness of the lamina, and again the resultant layer of resin is cured by the laser beam so as to produce the physical equivalent of the next lamina in the CAD file. The process is repeated until the desired solid object us produced. Supporting structures can be added via the software: these structures are a part of the composite data file and are xe2x80x9cgrownxe2x80x9d with the model required. On completion, the model is further treated, any supporting structures are removed, and the object is finished, to a produce smooth surface, by hand. It is highly advantageous that the object can be produced directly from a CAD design in a matter of days.
Other methods for rapid prototyping are Laminated Objective Manufacture (LOM) and Selective Laser Sintering (SLS). LOM involves computer driven cutting and lamination of thin paper sheets which are assembled as layers to produce a 3model. SLS involves the direct sintering of polymeric particles or of a metal composite in a layered fashion to produce 3D objects.
Prototypes can also be made by direct casting of glass fibre (GRP) models. The models are themselves cast from a moulding of the original clay prototype produced by a designer/stylist. GRP castings or other resinous castings can be taken from such (untextured) production mould tools, as well as from directly machined resin blocks. In the latter instance, CAD data can be used to drive a computer controlled (CNC) milling machine which automatically follows the contours of the CAD model, cutting away the resin (or other machinable material such as hard wood) to build up a 3D model of the prototype, often referred to as a mandrel. The moulding tools, typically in flexible silicone or hard epoxy, are cast from the mandrels. The moulding tools can then be used to produce multiple copies of the (untextured) mandrel.
None of these methods is able to properly impart a textured surface finish on to the prototype.
The present invention provides for rapid phototyping for textured-surface articles, including non-moulded articles, giving authentic pre-appreciation of both appearance and feel.
Furthermore, the present invention provides methods by which copies of such textured rapid prototypes can be made.
The invention comprises a method for simulating the apperence of an article having surface texture comprising the step of applying a textured skin having a surface texture to a prototype to produce a textured prototype, thereby to simulate the appearance of the article having surface texture.
The invention further comprises a method for producing copies of a textured prototype comprising the steps of:
applying a textured skin having a surface texture to a prototype to produce a textured prototype;
producing a mould of the textured prototype;
and using the mould to produce said copies.
The skin may comprise a skin layer with relief material attached thereto as a surface texture. The skin layer may constitute a release backing peeled off the prototype after application of the relief material thereto. The relief material may be preferentially adhered to the prototype to enable peel off of the release backing.
However, the skin layer may be soluble and be dissolved after the relief material is adhered to the prototype. The skin layer may be soluble in a paint which is applied after application to the prototypexe2x80x94the skin layer then becomes absorbed into the paint layer.
The skin may be burnished on to the prototypexe2x80x94this may be done before and/or after removal of the skin layer; if done before, burnishing serves the purpose of improving adhesion to the prototype and helping to smooth out any imperfections in application. Burnishing may be effected by a densely-bristled brush, though other burnishing tools may be found more appropriate to specific patterns.
As to patterns, the surface texture may be a random pattern texture, such as the popular leather and woodgrain finishes. A textured skin suitable for such finishes is commercially available glass engraving resist, in which a resist pattern is carried on a release sheet for application to a glass surface which is then sand blasted, the glass surface being eroded except beneath the resist which is then removed. In the present application, the resist material becomes part of the textured surface of the pre-textured prototype.
The method of the invention is particularly advantageous, however, with geometric patterns used as texture. Such patterns can be readily created by a CAD arrangement or like system which can control a cutting arrangement to cut the pattern into sheet material e.g. vinyl plastics sheeting. Such sheeting may be presented (in different thickness) on a release backing from which cut sheet may be separated, by differential bonding, on to a separate release sheetxe2x80x94there being then xe2x80x98positivexe2x80x99 and xe2x80x98negativexe2x80x99 versions of the pattern. Either release sheet then forms the skin layer of the textured skin.
Whilst the overall effect of a randomxe2x80x94leather, woodgrain etc-pattern may be visualizable by skilled designers, the way a regular geometric pattern texture sits on a curved surface is less easy to imagine. Indeed, difficulties are experienced in engraving even moderately complicated moulds with geometric pattern textures as a resist-carrying backing sheet usually has to be creased to fit the mould. Often, a regular geometric texture simply cannot be applied because of the difficulties of engraving the mould, this explaining a preponderance of random textures, principally leathers.
However, for prototyping purposes as disclosed herein, the skin may be arranged to be stretchable to fit without creasing on to the prototype and the texture is imparted to the skin (as by a CAD arrangement) in distorted fashion to compensate for skin stretching to fit the prototype.
The prototype itself may or may not be moulded. A non-moulded prototype may be produced by stereolithography, laminated object manufacture or selective laser sintering.
The step of producing a mould of the textured prototype may comprise casting the textured prototype in a mould forming material, which may be silicone rubber.
The step of producing a mould of the textured prototype may comprise a slush moulding process in which a metal coating is electroformed onto the textured prototype or a replica thereof. The metal may be nickel.
The step of producing a mould of the textured prototype may comprise a moulding process in which metal is sprayed onto the textured prototype or a replica thereof to form a metal shell.